Jerusalem Post

ByMAARIV ONLINE

Recent studies challenge the concept of “calories in versus calories out” and highlight surprising factors – from meal timing to chewing – that influence weight, satiety, and metabolic health.

For years, weight management was perceived as a simple equation: How many calories go in versus how many calories are burned. However, recent studies suggest a far more complex picture. It turns out that the human body is not merely a “calorie calculator,” but a dynamic biological system that responds to food in different ways depending on the timing of eating, the rate of consumption, the structure of the food, and even the composition of gut bacteria. This means that two people can eat the same food, in the same quantity, and experience completely different effects on weight and metabolic health, according to a study published on the BBC network.
The biological clock on the plate

One of the prominent factors emerging from the research is meal timing. Consuming the majority of calories in the morning hours has been linked to more efficient weight loss compared to eating later in the day, even when the total number of calories remains the same.

In addition, reducing the eating window – meaning shortening the time between the first and last meal of the day – may reduce total energy intake and even lead to a reduction in body fat. Snack timing also matters: Eating late at night has been associated with higher levels of blood sugar and “bad” cholesterol, and with an increased risk of obesity and heart disease. These findings align with a developing research field called chrononutrition, which examines the connection between the body’s biological clock and digestion and metabolism processes.
Eat slowly – and gain more

Not only when you eat matters, but also how. Eating pace is emerging as a central factor affecting the feeling of fullness and the amount of calories consumed. Eating slowly allows the body to activate natural satiety mechanisms. Hormones that regulate hunger and fullness are released gradually and reach their peak only after dozens of minutes. When eating is done quickly, the body cannot “keep up,” resulting in excessive food intake. Beyond that, slow eating has also been linked to better blood sugar balance, while fast eating may lead to sharper spikes in glucose – a significant risk factor over time.

When texture determines calories

Another aspect that challenges the simple calorie concept is food structure. Not every calorie is absorbed to the same extent, and this also depends on the way the food is served and consumed.

Whole and dense foods, such as nuts, are not always fully digested – especially when they are not chewed well. In contrast, ground, crushed, or ultra-processed foods break down much more easily, and the body absorbs more calories from them in a short period of time. This means that food texture – not just its caloric value – affects the feeling of fullness and the amount of energy the body actually extracts.
Everyone responds differently

Perhaps the most significant finding is the degree of variation between individuals. Studies indicate that the body’s responses to food vary considerably from person to person, even when it is exactly the same food. These differences are attributed, among other things, to the composition of the microbiome – the population of bacteria in the gut. Each person has a unique “microbial signature,” which influences how food is broken down and the metabolic responses that follow.
Thus, a certain food may cause a sharp rise in blood sugar levels in one person, while in another the effect will be much more moderate. These insights strengthen the approach of personalized nutrition, which takes into account the biological differences between people.

Conclusion: Complexity instead of simplicity

Despite the growing complexity, the central message does not cancel out the basic principles of nutrition. A varied diet, rich in fiber, alongside reducing the consumption of sugar, salt, and fat – is still considered a central recommendation.
However, recent research emphasizes that the path to health and a healthy weight is not uniform for everyone. Beyond the number of calories, attention should also be paid to the way of eating, timing, and food structure. Ultimately, the question may not only be “how much we ate” – but also “when, how, and in what form.”